1. Used for I2C communications. SCL is the clock, SDA is the data line. Master generates clock and outputs data, master generates clock and slave responds with data. An example of a I2C device is the DS1307 real time clockhttp://www.dipmicro.com/store/DS1307N2. Interrupts used to capture signal that needs to be responded to quickly.3. Tx & Rx used for serial communications where the receiver creates its own timing to determine when the data bit being transmitted is to be sampled, gnerally 16 samples per bit.Usage:Serial.begin(9600); // used in void Setup() to start the serial library

Transmit side:Serial.print("hey there"); // sends out a message

On receive side, fill an array with incoming data - Very basic usage, really needs expanding to be useful

1.What is SCL and SDA pins for? Are these some how helpful when integrating into a project?

The SCL and SDA pins are for I2C (aka IIC, TWI) communications, which permits multiple peripherals to be connected to the AVR using only two pins. It's sort of a mini-network; each external I2C peripheral has an address. It's "medium speed" (400kbps), widely used by things like A2D converters, external EEPROM memories, "IO expanders" and similar.The reason that these pins were added to the Arduino connector area is that they aren't always on the same pins of different microcontrollers. For example, SDA shares PC4 on the Atmega328 used on Uno (normally one of the analog pins), and PD1 on the mega32u4 used on Leonardo. By having separate connector positions on the board, you can (theoretically) connect i2c peripherals in the same place on different boards, and have "low-effort" compatibility using an appropriate library.

Given the amount of peripheral devices that use a 4 pin connector for I2C it sure would have beennice if the board had a set of 4 holes for a header/connector for the I2C pins that included power like the Seeeduino boards.That also allows it to be used with other non i2C shields.

What is polarity for external power supply socket?Is GND around and + in the middle?

thanks

There is no jumper pin required for using external power. There is an electronic voltage selector circuit on the board that detects if there is DC voltage on the external power connector (or the Vin) pin of 7.5 to 12vdc. If there is both USB power and external power available the circuit gives priority to the external voltage and switches off the USB power, however the USB communication is still available. And yes the center pin is the positive voltage and the sleeve is negative, however there is a series wired diode in the circuit that prevents board damage if one accidentally plugs in reverse polarity voltage, the board won't work as such, but there will be no damage done.

I like the hackability of the board who's pic is posted 1 post above they even thought about the crystal place there if in case one needs to clock it at a different rate rather than on whcih rate the resonator actually is.

"Real Men can Accomplish Anything"

- skype : nishants5 ਫ਼ਤੇਹ ਕਰੁਂ!www.winacro.com

WinstonP

It might be nice to be able to program the Atmega16U2-MU to be able to load sketches through it's ISP connector.Maybe even chain to subroutines in the Atmega16U2-MU's storage memory. Maybe future RTC built onto the next UNO revision.

IHNTA except "thank you". This thread was my first foray into the forums (complete newbie, curious about the pins not mentioned in Getting Started...) and delighted to find that you guys are helpful, clear, and above all patient. It almost makes me want to have a real problem so I can ask a question

mcwhorpj

I apologize for this silly question, but I have had some difficulty figuring it out and hope you can give me help. The VCC connection on the ICSP header (on the right side of your picture) . . . can you power the arduino through this pin? If so, can you power it with an unregulated source. Or, is this pin for providing power to other components. Just looking for clarification on what I can do with VCC on this pin. Thanks!